The present invention relates to an elongated tubular member having electrical conductors disposed therein. The tubular member is capable of transmitting both a fluid medium and electrical power to a remote location. The term elongated is used to refer to tubular members of at least 1000 ft. or more in length with the members being fluid-tight sothat the fluid can be transmitted to the remote location.
The tubular members of the present invention are particularly useful in the steam quality measuring systems disclosed in U.S. Pat. Nos. 4,581,926 and 4,736,627. These patents disclose methods and apparatus for measuring the quality of steam being injected into a subterranean formation to enhance the recovery of heavy crude deposits from the formation. Steam is the most widely used thermal recovery method where it is desirable to heat heavy crude deposits to more efficiently produce them. The patents require both the transmission of electrical power to the measuring apparatus and the transmission of signals from the apparatus. In addition, the apparatus zegulres the transmission of a purge gas to the downhole measuring apparatus to exclude borehole fluids from the apparatus.
The most convenient way to supply both the purge gas and the required electrical conductors is to enclose the electrical conductors in a tubular member that is stored on a suitable reel or drum. Thus, the measuring apparatus can be lowered into the borehole and the tubular member unspooled from the storage drum. This provides a simple means by which a single member can be used to support the measuring apparatus and lower it into the borehole. The tubular member is used to supply both electrical power and purge gas to the instrument. Alternative to this arrangement would be the use of separate electrical conductors and a tubular member. This would require storage on separate reels and the feeding of the electrical conductors and tubular member simultaneously into the borehole. This would be a complicated arrangement, particularly since it is necessary to feed the members through a wellhead lubricating system since the wells must actually be in production to obtain measurements. Since flow measurements are being made, the steam must be continuously injected so the well will remain under pressure. This requires the use of wellhead lubricators to maintain pressure in the well and prevent the escape of steam as the measuring equipment is inserted into the well.
It is, of course, possible to feed electrical conductors through preformed tubular members to provide the required combination of a tubular member and electrical conductor. While this is possible, it is normally not possible to feed the electrical conductors through the length of the tubular member required in well logging operations. Obviously, after transiting a few hundred feet of electrical conductor through the tubular member, the friction between the electrical conductor and the wall of the tubular member would prevent further feeding of the conductors. The use of short-length sections would require the making of numerous connections as the sec-ions are fed into the well. This is time consuming and would increase the probability of an ineffective electrical connection.
In addition to the problem of providing the tubular member with the electrical conductors disposed therein, there is also the problem in thermal injection wells of providing for temperature compensation between the different materials used for the electrical conductors and the tubular member. Normally, injected steam will have a temperature of 400.degree. F. to 500.degree. F. and a pressure of 200 to 600 psi and the tubular member must be capable of withstanding this temperature and pressure. In addition, many wells have a corrosive atmosphere that requires the use of corrosion resistant materials. An obvious choice is the use of one of the alloy steels that are corrosion resistant and have a high strength at elevated temperatures. Obviously, the electrical conductors should be copper to provide good electrical circuits. Since most alloy steels and copper have significantly different coefficients of thermal expansion, some means must be provided for compensating for the greater expansion of the copper conductors in the alloy steel tube. If no means are provided for compensating for the expansion of the copper conductors, the greater length of the conductors will cause them to tend to fall to the bottom of the tubular member as it is lowered into the borehole In extreme cases the conductors could eventually plug the bottom of the tubular member. In addition, it is possible that when the tubular member is withdrawn from the borehole, spooled on the storage drum and allowed to cool to atmospheric conditions, the copper, in cooling, will break some of the conductors due to contraction and the inability of the bunched-up conductors to freely move within the tubular member.